Field of the Invention
Embodiments of the present invention generally relate to driving loads in electronic devices, or more specifically, driving a transmitter signal in a capacitive sensing device.
Description of Related Art
Input devices including proximity sensor devices (also commonly called touchpads or touch sensor devices) are widely used in a variety of electronic systems. A proximity sensor device typically includes a sensing region, often demarked by a surface, in which the proximity sensor device determines the presence, location and/or motion of one or more input objects. Proximity sensor devices may be used to provide interfaces for the electronic system. For example, proximity sensor devices are often used as input devices for larger computing systems (such as opaque touchpads integrated in, or peripheral to, notebook or desktop computers). Proximity sensor devices are also often used in smaller computing systems (such as touch screens integrated in cellular phones).
To operate electronic devices, such as displays and input devices, it is often necessary to drive a load. The time required to drive the load may be a function of a resistance and/or a capacitance (i.e., an RC time constant). Conventional driving methods use two voltage levels (i.e., a high level and a low level). For example, a transmitter electrode in a touch sensor device may be driven with a waveform comprising a series of square waves. The frequency of the waveform, however, may be limited because it is necessary to provide a sensing cycle long enough to allow the transmitter electrode to “settle” to a desired value. Settling time tends to increase as the resistance and/or capacitance increases. For example, driving a load using thinner and longer electrical conductors may increase resistance, and driving a physically larger load may increase capacitance. As a result, the RC time constant may be longer. However, long settling times may be undesirable due to noise and system performance which may require operating an electronic device at high frequencies. Accordingly, it is desirable to decrease settling times of electronic devices.